1. The Field of the Invention
This invention relates to a method for preparing a high 1,4-cis polybutadiene having a controlled cold flow. More specifically, this invention relates to a novel method for preparing a high 1,4-cis polybutadiene having a controlled cold flow that involves initiating a polymerization of 1,3-butadiene using, as a catalyst, a complex comprising a neodymium compound, a halogenated organoaluminum compound or a halogenated organic compound, and an organoaluminum compound, and then adding an organoborane compound to the reaction system after a predetermined time period, thereby efficiently controlling the cold flow of high 1,4-cis polybutadiene.
2. Related Prior Art
The high 1,4-cis polybutadiene prepared in the presence of a neodymium catalyst, as a major catalyst, that is one of rare earth metal salts (i.e., metal salts from lanthanum (57) to lutetium (71)) exhibits more excellent properties such as high 1,4-cis content, high molecular weight, and narrow molecular weight distribution, compared with the high 1,4-cis polybutadiene prepared in the presence of a transition metal salt (e.g., nickel, titanium or cobalt salt) as a major catalyst. However, such a high 1,4-cis polybutadiene results in a high cold flow due to its molecular structure having a high linearity, causing poor storability, workability and processability.
The cold flow of high 1,4-cis polybutadiene is of a great importance in relation to storability, workability and processability of the product. An excessively high cold flow may function as a factor in the serious deterioration of storability (i.e., causing the product to flow out of the packing material and contaminating the product with various impurities to deteriorate the properties of the product), workability (i.e., causing the product to flow out of the packing material and adhere to the same product of another packing material, thereby changing the weight of the product packed according to a standard and causing a need for unpacking and reweighing the product to reduce the productivity), and processability. Thus when the product is packed in a defined standard, the ability of the product to maintain the original packed shape for a predetermined time period regardless of weight, pressure and elapsed time is one of the very important properties to those manufacturers that produce other products using the high 1,4-cis polybutadiene.
Many conventional polybutadiene preparation methods using a rare earth metal salt such as neodymium as a catalyst have been reported as follows. U.S. Pat. No. 5,686,371 discloses a preparation method of high 1,4-cis polybutadiene using, as a catalyst, a complex prepared by aging a mixture of a neodymium salt compound, a silicon halide compound, an organoaluminum compound, and a diene compound. U.S. Pat. No. 4,699,962 discloses a preparation method of high 1,4-cis polybutadiene using, as a catalyst, a complex prepared by mixing a neodymium hydride compound, a chlorine-containing compound, an electron-donor ligand, and an organoaluminum compound. European Patent No. 127,236 discloses a 1,3-butadiene polymerization method using, as a catalyst, a complex prepared by mixing a neodymium compound, an organohalide compound, an organic compound containing a hydroxyl group, and an organoaluminum compound. European Patent No. 375,421 and U.S. Pat. No. 5,017,539 disclose a preparation method of high 1,4-cis polybutadiene using, as a catalyst, a complex prepared by aging a mixture of a neodymium compound, an organohalide compound, and an organoaluminum compound at a temperature of below 0° C.
In addition, U.S. Pat. No. 5,567,784 discloses a preparation method of 1,4-cis polybutadiene that prepares 1,4-cis polybutadiene in the presence of a non-polar solvent using, as a catalyst, a complex comprising a neodymium carboxylate compound, an alkyl aluminum compound, and a halogen-containing compound, and then adds sulfur chloride to lower the cold flow, thereby improving the processability. This method involves adding sulfur chloride after removal of non-reacted 1,3-butadiene so as to diminish the smell of the added sulfur chloride, but has the difficulty in eliminating completely the odor of sulfur chloride.
European Patent No. 0 386 808 A1 discloses a preparation method of 1,4-cis polybutadiene that involves preparing a 1,4-cis polybutadiene in the presence of a non-polar solvent using a catalyst comprising a neodymium carboxylate compound, an alkylaluminum compound, and a halogen-containing compound, and then adding a phosphorous trichloride (PCl3) to lower cold flow, thus improving processability. But, in this method, the Mooney viscosity of the product greatly increases with an increase in the amount of PCl3.
U.S. Pat. Nos. 4,906,706 and 5,064,910 disclose a method that uses, as a catalyst, a complex prepared by mixing a rare earth metal salt compound, a Lewis acid and/or a Lewis base, and an organoaluminum compound with/without a diene compound, and then aging the mixture. The polymerization is performed using the aged catalyst, and isocyanate, carbon disulfide, an epoxy compound, or an organotin halide compound is added to the produced 1,4-cis polybutadiene to deform the structure of 1,4-cis polybutadiene, thereby improving cold flow and properties.
U.S. Pat. Nos. 3,346,549 and 4,204,969 disclose a method that polymerizes an olefin compound using both a halide and a sulfur chloride compounds and uses the resultant polymer as an additive of a lubricant oil to enhance the characteristics of load carrying, extreme pressure, and viscosity index.
However, these conventional approaches provide incidental problems such as the increased Mooney viscosity of the product, an odor (bad smell), and a reduction in both 1,4-cis content and polymerization yield, thus having difficulty in controlling efficiently the cold flow of high 1,4-cis polybutadiene.